1. Field of the Invention
This invention relates generally to microwave interactive packaging materials, and more specifically to the introduction of indentation patterns into such materials to provide moisture venting and improved heating characteristics.
2. Description of the Related Art
Scoring and molding of stiff packaging materials during the manufacture of packaging products is a standard practice in the packaging industry. For example, stiff packaging material, e.g., paperboard, is regularly scored to create fold lines for easier manipulation of the packaging material into different configurations, for example, boxes or trays. Similarly, flat packaging material may be manipulated by compression molding devices to form product packaging with sidewalls from the originally flat material. Such compression molding techniques may be augmented by scoring areas along which the sidewalls are formed before placing the packaging material into a compression mold. These scoring and molding techniques are frequently used in the food packaging industry to create boxes, pans, trays, and other packaging for food products. The score lines created in these processes are typically on the order of 1 mm wide or more.
Another use of such scoring and molding techniques in the food packaging industry is to increase the rigidity of the packaging material. For example, configurations such as parallel ribs, concentric circular channels, and perimeter depressions have been variously molded into flat packaging substrates, e.g., paper or paperboard, to create greater resistance to bending moments of the packaging material. Generally such molded features are quite large, with widths typically ranging from one-quarter to one-eighth of an inch. Non-functional features are also regularly molded into food packaging, for example, designs or patterns that increase the aesthetic attributes of the packaging or indicia that assists with the marketing or identification of the product. In order to create such molded features in a packaging substrate, either functional or aesthetic, matched male-female embossing tooling is generally used. Such tooling is usually “special purpose,” that is it is built for the specific use desired and can therefore be quite expensive.